1. Field of the Invention
The present invention relates generally to spring probes and more particularly, to a sleeve-type spring probe and a probe card having the spring probe.
2. Description of the Related Art
FIG. 1 is an exploded plan view of a conventional spring probe 11 which includes a needle 12, and a spring sleeve 13 sleeved onto the needle 12. FIG. 2 is a schematic sectional view of a probe card 14 using the spring probe 11. For the convenience of illustration, FIG. 2 is not drawn to the same scale with FIG. 1. The probe card 14 includes a circuit board 15 and a probe device 16. The circuit board 15 may be the circuit board adapted for being electrically connected with a tester (not shown). Alternately, the circuit board 15 may be a space transformer disposed between the probe device 16 and the circuit board (not shown) adapted for being electrically connected with a tester (not shown). The probe device 16 includes a probe seat 17 and a plurality of probes 11. For the convenience of illustration, only a small part of the circuit board 15 and the probe seat 17 and one of the probes 11 are shown in FIG. 2.
The needle 12 and the spring sleeve 13 of the spring probe 11 are connected in a way that a connection segment 132, which is provided near the bottom end of the spring sleeve 13, is pressed against the needle 12 and fixed to the needle 12 by welding, such as spot welding. As a result, the connection segment 132 has two convex portions 134 resulted from deformation of the connection segment 132 in the aforesaid press fixing process, and the convex portions 134 protrude over an outer circumferential surface 136 of non-pressed parts of the spring sleeve 13.
The probe seat 17 is composed of upper, middle and lower dies 171, 172, 173; however, the probe seat 17 may be provided without such middle die 172 but composed of the upper and lower dies 171, 173 only. The dies 171, 172, 173 have a plurality of through holes 171a, 172a, 173a respectively, which jointly compose a plurality of installing holes 174 for the installation of the spring probes 11 (only one of the installing holes 174 is shown in FIG. 2). In order that the spring probe 11 can be installed into the installing hole 174 through a top surface 175 of the completely assembled probe seat 17 and rotatable unlimitedly in the installing hole 174 when probing a device under test (hereinafter referred to as the “DUT”), the installing hole 174 is configured as a circular hole with a radius greater than the maximum distance between each convex portion 134 and the center of the spring probe 11.
After the probe device 16 is assembled completely, the circuit board 15 is disposed on the top surface 175 of the probe seat 17. The top end of the spring sleeve 13 is electrically connected with a contact pad of the circuit board 15. The bottom end of the needle 12 is adapted to probe a contact pad of the DUT. Specifically speaking, the top end of the spring sleeve 13 is abutted against the circuit board 15, and the spring sleeve 13 is provided with two spring sections 138 which are compressible elastically. Besides, the connection segment 132 of the spring sleeve 13 is fixed to the bottom section of the needle 12, and a clearance 18 is provided between the top end of the needle 12 and the circuit board 15, i.e. between the top end of the needle 12 and the top end of the spring sleeve 13. Therefore, when the bottom end of the needle 12 contacts the contact pad of the DUT and correspondingly feeds forward, the needle 12 will retract backwards, such that the spring sleeve 13 will be compressed. In this way, the probe 11 can positively contact and electrically connect the contact pad of the DUT; besides, by means of the cushioning effect provided by the spring sleeve 13, an exceeding contact force, which may cause damage or heavy wear of the contact pad of the DUT or the needle, can be prevented.
The outer radius of the aforesaid spring probe 11 is very small, which is usually in a range of several tens micrometers to a little more than one hundred micrometers, and the aspect ratio of the spring probe 11, i.e. a ratio of height to width thereof, is very large, which is usually in a range of 10:1 to 100:1. Besides, except for the convex portions 134 which are relatively closer to the inner wall of the installing hole 174, the other parts of the spring sleeve 13 are quite distanced from the inner wall of the installing hole 174. Therefore, the spring probe 11 is liable to deflect and bend when the bottom end of the needle 12 receives external force, as shown in FIG. 3. This phenomenon may result in problems of inaccurate alignment, unstable probing pressure, and the tendency of fracture of the probe. If the probe is fractured, more problems will arise, such as difficulties in maintaining and replacing the probe. Further, because the installing hole 174 has a large radius, which makes the adjacent probes quite distanced from each other, the fine pitch requirement of the high-density probe card can hardly be fulfilled. Furthermore, when the circuit board 15 is not yet disposed on the top surface 175 of the probe seat 17, and the probe seat 17 is posed upside down, the spring probe 11 will fall from the probe seat 17, causing inconvenience to the assembly of the probe card.
When the test signal is transmitted from the DUT to the circuit board 15 through the spring probe 11, the current of the test signal may be transmitted from the bottom end of the needle 12 to the top end of the needle 12 and then transmitted to the circuit board 15 through the topmost non-spring section 139A. Alternately, the current of the test signal may be transmitted from the bottom end of the needle 12 to the connection segment 132 of the lowest non-spring section 139B, then transmitted from the non-spring section 139B to the non-spring section 139A through the spring sections 138, and finally transmitted to the circuit board 15. In other words, the spring probe 11 has two signal-transmitting paths, which may produce unexpected variation and bring the spring probe 11 unstable in performance. Besides, in the grinding process for grinding the pinpoints of the spring probes 11 to make the pinpoints of all probes 11 be located on a same imaginary plane, the spring probes 11 will spin and thereby affect the grinding force, which will make the spring probes 11 grinded in the same grinding process have unequal lengths. Furthermore, for a good heat-dissipation effect in fixing the spring sleeve 13 to the needle 12 by welding, the non-spring section 139B should be provided with sufficient length. On the other hand, for the non-directionality in sleeving the spring sleeve 13 onto the needle 12, the non-spring section 139A should be provided with equal length to the non-spring section 139B. Such requirements not only limit the flexibility in designing the spring probe 11, but also make the spring probe 11 be configured having quite lengthy; i.e. the spring probe 11 is unable to be configured shorter.